This invention relates generally to a bending device for use in an endoscope or the like, and more particularly to an improved bending device designed not to cut an operating wire passing through the interior of the bending device.
A bending device for an endoscope as shown in FIG. 13 comprises a number of cylindrical segments a arranged in a row. The left end of each segment a is pivotally connected by pintles b to the right end of the left adjoining segment a at two points circumferentially spaced 180.degree. from each other. Each segment a has a pair of inwardly-directed, stamped guide portions c circumferentially spaced 90.degree. from the pintles b. Operating wires e are passed through the guide portions c.
In the above construction, when the lower operating wire e is pulled while the upper operating wire e is loosened, each segment a is pivotally moved relative to its adjoining segment a, so that the bending device is bent or curved downwardly. In contrast, when the upper operating wire e is pulled, the bending device is bent upwardly.
In the above bending device, when the operating wire e is cut off, it is impossible to bend the bending device. Therefore, it is desired to reduce the possibility cutting of the operating wire and thus prolonging the lifetime of the operating wire.
In a bending device disclosed in Japanese Laid-Open Utility Model Application No. 61-188701, opposite ends of a guide portion c are chamfered as at f as shown in FIG. 14. Alternatively, the diameter d of a hole in the guide portion c is increasing progressively from its central portion toward the opposite ends thereof, as shown in FIG. 15. However, such arrangements have hardly contributed to the prevention of the cutting of the operating wire. The reasons for this will now be described.
As shown in FIG. 13, to bend the bending device downwards, the lower operating wire e is pulled while the upper operating wire e is loosened. Therefore, the operating wire e that may be cut off is the lower one. Therefore, the lower operating wire e will not be in contact with the guide portions c. Therefore, the configurations of the guide portion c as shown in FIGS. 14 and 15 are insignificant.
The pulled operating wire e is bent by opposite ends A.sub.1 and A.sub.2 of that portion (i.e., wire guide surface portion) of the inner peripheral surface of each segment a along which this operating wire is extended. Since this wire guide surface portion extends straight, the pulling force of the operating wire e concentrates on the opposite ends A.sub.1 and A.sub.2 of the wire guide surface portion, so that the contact pressure on the operating wire with these opposite ends becomes very high. It is quite possible that the operating wire e may be cut off as a result of the repeated bending of the operating wire and the rubbing of the operating wire with the opposite ends A.sub.1 and A.sub.2 of the segments a under a high contact pressure.
Referring to other related art, U.S. Pat. Nos. 3,190,286 and 4,432,349 describe a technique in which opposite ends of each wire guide surface portion with which a pulled operating wire is contacted are chamfered. However, the wire guide surface portion except, for its opposite ends is extended straight, and this straight portion does not bear the pulling force of the operating wire at all. Therefore, the pressure of contact between the opposite ends of the straight portion of the wire guide surface portion and the operating wire becomes high, and as a result the lifetime of the operating wire cannot be prolonged.